Technical Field
The present invention relates to ink, an inkjet recording method, and inkjet recorded matter.
Description of the Related Art
Since inkjet printers are relatively quiet, enjoy low running costs, and are capable of printing color images with ease, they are now widely used at home as an output device of digital signals.
Technologies of printing images on packaging materials for food, beverages, commodities, etc., which utilize inkjet have also been developed.
For such usage, non-porous recording media such as plastic film are used and ink for such media have been developed. In the case of most of such packaging materials, generally, images, texts, etc. are printed first on the rear side of a plastic film and thereafter an adhesive is applied to the printing layer and a heat sealable film is attached to the printing layer to obtain a laminate packaged article. However, in the case of a package of fruit and bread, a packaging material having a plastic film surface on which images, texts, etc. are directly printed is popular in terms of reduction of packaging cost.
In the latter case (so-called front surface printing), the printing layer directly contacts, for example, the printing layer of an adjacent packaged material or a box and scraped by abrasion therebetween, which may cause the printing unclear. Therefore, abrasion resistance is demanded for such printing.
Therefore, practically-usable ink for direct printing on the surface of a plastic film is mostly a two-liquid curable type, a UV curable type, or a vehicle type using an organic solvent which is expected to have at least slight permeability to a plastic film substrate.
These types of ink have problems about process, facility, and handling of harzardous material. Also, it may cause health problems.
Therefore, a single liquid type ink requiring no curing treatment is proposed which is capable of forming a strong film on the surface of plastic film while it is not solvent type ink (including a monomer solvent) but an aqueous type.
For example, inkjet ink is proposed which includes polymer colloid particles formed by partially copolymerizing a monomer containing an acid functional group such as (meth)acrylic acid and carbon black pigment particles graft-bonded with a second polymer by the ftuictional group on the surface in an aqueous liquid vehicle including a cosol vent having a boiling point of 285 degrees C. or lower accounting for 50 percent by mass or less.
In addition, aqueous inkjet ink is proposed which includes a copolymerized resin synthesized from monomers including methyl methacrylate, an acid monomer, an acrylic acid alkyl ester having an alkyl group having 2-4 carbon atoms, and an acrylic acid alkyl ester having an alkyl group having 6-12 carbon atoms, a pigment, water, a water-soluble organic solvent, and a silicone-based or fluoro surfactant. The copolymerized resin is an acrylic resin having an acid value of 50-120 mgKOH/g, a glass transition temperature (Tg) of 30-110 degrees C., and a mass average molecular weight (Mw) of 20,000-80,000.
Coverage film formed of acrylic resin ink or paint is known to impart gloss and sharp colors. However, such coverage film is disadvantageous in terms of flexibility of the film and attachability with an undercoating layer.
Also, aqueous ink is provided which uses as an emulsion of chlorinated polypropylene or a copolymer of polypropylene and acrylic as a binder resin. Basically, this uses an acrylic-based resin.
To improve attachability with the undercoating layer, an aqueous paint having durability is mainly introduced which uses polyurethane-based resin instead of an acrylic resin. This is currently the main stream of durable aqueous paint and applied to ink to the present day.
Of plastic film for soft packaging, polypropylene (PP) film is mainly used. Since polypropylene is an inexpensive material having excellent properties with regard to formability, chemical resistance, heat resistance, etc., stable increase in demand for propylene film is expected in the future. However, unlike a synthesis resin having a polarity, polypropylene is a non-polarized and crystal material. Therefore, aqueous ink is easily repelled thereon, which makes forming images on such a film difficult.